This application claims the priority of German patent document 103 18 580.1, filed Apr. 24, 2003 (PCT International Application No. PCT/DE2004/000853, filed Apr. 22, 2004), the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method and apparatus for simultaneous detection and analysis of at least two electromagnetic signals, such as may be used in a spacecraft, in particular.
The term spacecraft in the sense of the invention includes all artificial bodies designed for use in outer space, including satellites, space probes, space shuttles, space stations or rockets. However, in principle, the method and apparatus can also be used for terrestrial applications. The term receivers in the sense of the invention includes all devices which are designed to receive and process electromagnetic radiation, for example, for the purpose of the data exchange between spacecraft, or between the spacecraft and earth stations, or between other objects, or also for the purpose of the detection, locating, measuring and/or observation of objects emitting electromagnetic radiation. Signals in the sense of the invention are represented by any type of electromagnetic radiation which can be detected by a receiver according to the invention, thus including radiation actively emitted by an object as well as passively scattered or reflected by an object.
German patent document DE 198 46 690 A1 discloses an optical receiver system which is constructed in the form of a combined earth-star sensor, and is used for observing the earth and the stars. From the obtained information, a three-axis attitude and position determination of satellites is permitted.
An optical receiver system for optical intersatellite connections is disclosed and described in detail in German Patent Document DE 198 47 480 A1. Such intersatellite connections are used for exchanging data between individual satellites, but can also be used to determine the attitude of a satellite, as in the case of German Patent Document DE 198 47 480 A1.
However, a problem arises in the case of arrangements from the state of the art when two or more electromagnetic signals that are to be detected simultaneously are mutually superimposed on a common detector. Here, it must be possible nevertheless to separate the individual electromagnetic signals sufficiently to permit a clear identification of the individual electromagnetic signals. Another problem is that a distortion of detected radiation images often occurs in the area outside the optical axis of the receiver. This is especially important when one of the electromagnetic signals must be determined with a particularly high precision. The state of the art offers no satisfactory solution for this purpose.
It is therefore an object of the invention to provide a method and a receiver apparatus for simultaneous detection and analysis of at least two electromagnetic signals, which eliminates the disadvantages of the state of the art.
This and other objects and advantages are achieved by the method according to the invention, which comprises the following steps:                Division of an input radiation image into at least two partial images        Projection of the partial images on a radiation detector; and        imaging the partial images on the radiation detector in such a manner that radiation intensities of the partial images are projected from the image center of the input radiation image to the edge of the radiation image on the detector.        
In this case, a planar expanded electromagnetic radiation signal is considered to be the radiation image signal, which radiation signal appears as an image and not only as in a largely punctiform shape when it is projected on the detector.
The advantage of the method according to the invention lies in the fact that the radiation image, which as an expanded radiation signal is less susceptible to distortions, is displaced into edge areas, so that the area around the optical axis can be utilized for the—simultaneous—detection of less expanded signals, in a more precise manner. This applies particularly if, in addition to the radiation image, the exact position of another signal of a smaller expansion is to be detected. In addition, mutual interference of the signals that are to be simultaneously detected can be avoided (or at least diminished) as a result of the displacement of the radiation intensities of the partial images into the edge area. This is particularly applicable when the radiation intensities of the radiation image are approximately equally to or even greater than the radiation intensity of the at least one other signal. The detector surface can also be used more effectively by the displacement of the radiation intensities from the image center of the radiation image into the edge area.
The projection of the radiation intensities of the partial images from the image center of the input radiation image to the edge of the radiation image can take place in particular if the partial images of the input radiation image are reflected. However, as an alternative, it can also be provided that the partial images of the input radiation image are displaced in the direction of the image edge.
The division of the input radiation image can take place into any suitable number and shape of partial images which permit the displacement of the radiation intensities from the image center of the input radiation image to the edge of the radiation image. Thus, in the case of a square input radiation image, the input radiation image can be divided into four partial images, with imaging of the partial images such that radiation intensities are projected from the image center of the input radiation image in the direction of a corner of the radiation image on the detector. However, a division into only two partial images or into a larger number of partial images is also possible.
In principle, the method according to the invention can be used for all suitable types of electromagnetic signals, one of which is a radiation image signal. Thus, for example, a data communication signal can be detected as one of the electromagnetic signals, for example, in addition to a radiation image signal. A usage for this purpose can take place, for example, within the scope of data connections between objects, such as particularly spacecraft or the like. For this purpose, reference is also made to the statements in the introduction to the specification.
In a special application of the present method, it may be provided that radiation images of reference objects, particularly celestial bodies, are detected as radiation image signals. This can be provided particularly when an identification or position determination of certain reference objects, such as particularly celestial bodies, is to take place. The information thus obtained can be used, for example, to determine position and/or attitude information relative to the corresponding reference object. However, in addition to the detection of one or more reference objects, other electromagnetic signals, such as those of largely punctiform signal sources can also be detected. The latter may be used, for example, to obtain additional position information and/or attitude information, and also, for example, for the data communication.
In a special embodiment of the above-mentioned method, which is used particularly for spacecraft, radiation images of the earth and the stars are detected simultaneously and the image of the earth is divided into partial images. As a result, it is possible to detect the, as a rule, largely punctiform electromagnetic signals (which usually have a lower intensity) in the optical axis of the detector and therefore largely without any distortion. This arrangement permits a precise position determination of the stars. In contrast, the more expanded (and, as a rule, higher-intensity) radiation image of the earth is displaced to the edge of the detector, into an area outside the optical axis of the detector. Thus, a detection of the earth and the stars is permitted with a greater precision than in the state of the art while the mutually influencing of the respective signals is simultaneously reduced.
Another feature of the present invention is the provision of a receiver having a device for simultaneous detection and analysis of at least two electromagnetic signals by a joint detector, at least one of which is a radiation image signal. According to the invention, at least one radiation image splitter is provided for dividing the input radiation image into at least two partial images and projecting them onto a radiation detector. The latter is designed such that the partial images are formed on the radiation detector with their radiation intensities projected from the image center of the input radiation image to the edge of the radiation image on the detector. Analogously, the advantages which were illustrated for the method according to the invention are obtained for the receiver according to the invention.
In particular, the radiation image splitter can be designed such that the partial images of the input radiation image are reflected. However, the radiation image splitter may also be designed in such a manner that the partial images of the input radiation image are displaced in the direction of the image edge.
In the case of a square input radiation image, the radiation image splitter can particularly be designed such that the input radiation image is divided into four partial images, whose radiation intensities are projected from the image center of the input radiation image in the direction of a corner of the radiation image on the detector.
The receiver can also be constructed as part of a data communication device. For this purpose, reference is made to the statements concerning the method according to the invention.
The receiver can also be designed as a sensor for the detection of radiation images of reference objects, such as celestial bodies. In this respect, reference is also made to the statements concerning the method according to the invention. A combination with another detection method of signals, for example, for the data communication, can also be provided in the case of the receiver according to the invention. The receiver may be designed, for example, as a combined earth-star sensor.
In principle, the receiver can be designed for any suitable wavelength or any suitable wavelength range. In particular, it can be provided that the receiver is designed as an optical receiver.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.